Optimize mysql table, the safe way

perform further steps in screen mode:

screen -r

Execute the following SQL query:

create table history_text_tmp like history_text;

Stop backend:

systemctl stop zabbix-server

Execute these queries (this queries will change Zabbix schema, and may cause 1-2 seconds data loss):

rename table history_text to history_text_old;
rename table history_text_tmp to history_text;

Start backend:

systemctl start zabbix-server

Execute the following query (the query will shrink free / reserved space from allocated space for history_text_old table):

optimize table history_text_old;

Stop backend:

systemctl stop zabbix-server

Rename back:

rename table history_text to history_text_tmp;
rename table history_text_old to history_text;

Start backend:

systemctl start zabbix-server

Copy data from temporary table and then delete temporary table:

INSERT INTO history_text SELECT * FROM history_text_tmp;
DROP TABLE history_text_tmp;